Wafer carriers or baskets are much used in the manufacture of electronic devices. For example, during the manufacture of integrated circuits, semiconductor wafers are subjected to a variety of processing steps in which they are held in and transferred between plastic baskets or carriers. The baskets have slots to support the wafers by their edges in a spaced-apart arrangement so that scratching of the wafer surfaces is minimized. Such wafer carriers or baskets are well known in the art. Examples of such prior art carriers are the semiconductor wafer baskets manufactured by Fluoroware, Inc., Chaska, Minn. Prior art semiconductor wafer baskets are also described in U.S. Pat. Nos. 3,923,156, 3,961,877, and 4,471,716 which are incorporated herein by reference. As used herein, the words "carrier" and "basket" in connection with a device for holding wafers are intended to be synonymous.
During processing it is frequently necessary to transfer the wafers from one carrier or basket to another. This is most conveniently accomplished by placing an empty basket on top of the filled basket with the open faces together. Small round alignment pins and matching holes in the upper edges of the baskets align the wafer slots of the two baskets. The combination of the two baskets are then inverted so that the wafers roll and/or slide from one basket to the other. This procedure is referred to in the art as a "dump transfer" or "roll transfer". For the purpose of this invention it is not important whether transfer of the wafers from one basket to the other is by rolling or sliding, and the words "dump transfer" are intended to include all manner of rolling or sliding motions which may take place during the process of transferring the wafers from one basket to another. As a practical matter, it is desirable that the transfer process not introduce any scratches or other mechanical defects or contamination in the wafers.
While the prior art baskets have been extensively used, the small round alignment pins and holes provided for aligning the wafer slots during dump transfers have not proved particularly reliable. The pins are easily damaged or broken during use. Further, the operator using the basket or performing a dump transfer may not detect the presence of damaged or missing alignment pins, with the result that the baskets do not remain in alignment during the transfer operation and the wafers contained therein may be damaged or broken. Thus, the relatively poor reliability of the prior art carriers can result in significant manufacturing loss of the wafers being handled therein, particularly during transfer operations. Accordingly, a need continues to exist for an improved carrier and method for holding and transferring wafers, particularly semiconductor wafers.
It is an object of the present invention to provide an improved carrier for holding and transferring wafers, particularly semiconductor wafers.
It is a further object to provide an improved carrier having a dump transfer alignment means which is more robust and reliable than in the prior art.
It is an additional object of the present invention to provide an improved wafer carrier having a means for improved alignment of the wafer slots in the carriers being mated for dump transfer of wafers.
It is an additional object of the present invention to provide an improved process for dump transferring wafers, particularly semiconductor wafers.